One wastewater treatment (WWT) option is disinfection with ultra violet (UV) light to remove pathogens and some contaminants, but substances in treated wastewater, such as particles of solid matter, can absorb the UV radiation and reduce its disinfecting activity. This research identified the sources of substances which are not removed by standard WWT plant processes, and which impair UV disinfection. It was concluded that trade wastes are a major source of organic, non-biodegradable humic-like substances which pose more of a problem to UV disinfection than total suspended solids. A sensor-probe based method for analysing fluorescence (‘EEM-PARAFAC’) was found to be an effective way to evaluate amounts of humic-like substances in effluents, and this information will improve management of UV WWT.

This research was prompted by concerns that rooftop-harvested rainwater fed into household hot water services might expose the public to harmful pathogens such as salmonella. Householders can be exposed to untreated heated rainwater while washing and when this water is used to wash or prepare food. Water heated to 60°C and maintained at this temperature for several minutes’ kills most, but not all infectious pathogens. The problem is that many Australian hot water services operate at lower temperatures that do not kill enteric pathogens. In this study fewer than 5% of water samples collected from unheated rainwater tanks contained pathogens, but this relatively low frequency still poses a risk and is part of the reason that heated rainwater systems fail to meet existing guidelines for safety. Modifications that would improve safety include installing a device that prevents water cooler than 60°C leaving the storage tank and using cold potable water instead of cold rainwater for tempering or in mixer taps. UV disinfection devices attached to rainwater systems are an effective way to reduce health hazards to acceptable levels.